boar_d_laze wrote:One oft repeated internet opinion is that atmospheric burners transfer more gas odor to the beans than IR burners, so IR burners are better. Rich

Now that you mention it, I think I like the gas taste. I'll probably add it to my SCAA cupping chart this morning.

In comparison to the other North models, the TJ-067 exhibits a very high degree of refinement. I'm reworking a 2 kg roaster right now designed by someone else and instead of submitting endless engineering changes, I have begged Tim to get me 2, 3, and 5 kg roasters designed by the TJ-067 guy. There's always something to pick at, but he obviously knows how to set up a coffee roaster. They'll be slightly more expensive, but I'm reasonably certain they'll be worth it. We'll receive his 3 kg model in couple of months and we'll know for sure.

With all the IR speculation, because I'm slightly nonplussed by the burner arrangement, I briefly considered banging an IR burner into my 2 kg roaster. They are readily available and not terribly expensive. Marginally easier than TIG welding a larger copy of the stainless TJ-067 manifold, if I have clearance.

We'll see. We have a complete fab facility and machine shop, but I'm continually restraining myself from "perfecting" everything.

Grandpa used to say, "most things fix themselves or you get used to them", but I have to constantly remind myself to not let the perfect be the enemy of the good.

Anyone else have anything to chime in about IR roasting? My research seems to say that unless a heat exchanger is employed (unless it's a perforated drum), the heat from the IR burner doesn't heat up the convective air flowing through the drum as well, causing an inconsistent convection temperature across the beans.

Also, I don't know the orientation of the burner in the unit, and if it's directly below the drum, it could be a catch basin for chaff and other debris. Most seem to put it at the side and angle it towards the axle.

I have a Diedrich IR-1.
The IR burner is directly below the drum. Some chaff collects in the burner area and I vacuum it out about every 5kg or so, this would be very different with a perforated drum.
The IR-1 is rated at 8000btu/per hour at max pressure. What is someone's 1kg atmospheric burner rated at?
No I do not just set a gas pressure and control with airflow, I have very nice control of ROR with my gas pressure settings.
Diedrich air flow has 3 settings 20/80 50/50 and 80/20 so there is at least 20% airflow through the drum at all times.

Just my opinion but I feel my IR burner is very gentle on the beans, I have to try very hard to create roasting defects or maybe I am just that good, pretty sure it's the IR burner.

networkcrasher wrote:My research seems to say that unless a heat exchanger is employed (unless it's a perforated drum), the heat from the IR burner doesn't heat up the convective air flowing through the drum as well, causing an inconsistent convection temperature across the beans.

I've never read anything like that. Do you have any links to your sources?

germantown rob wrote:Diedrich air flow has 3 settings 20/80 50/50 and 80/20 so there is at least 20% airflow through the drum at all times.

At a guess, 20/80 is very close to the minimum necessary to maintain a negative pressure in the drum with a big charge.

Building that in is just good engineering on Diedrich's part.

Just my opinion but I feel my IR burner is very gentle on the beans, I have to try very hard to create roasting defects...

You're just being modest. I'll bet you could do it pretty handily if you only you'd put your heart in it.

That said, air heated by an IR burner to a particular temperature isn't markedly different from air heated by an open pot to the same temp.

Rich

boar_d_laze wrote: ...
I've never read anything like that. Do you have any links to your sources?
...
That said, air heated by an IR burner to a particular temperature isn't markedly different from air heated by an open pot to the same temp.

Rich, I may have had something indirectly to do with Mark's comments. I had commented earlier on this thread and some of my thoughts on this have developed based on my collective understanding of the Huky design and heating element roasters such as the HotTop and Behmor.

Basically, IR burners pump out, well, IR energy in the form of radiation to heat surfaces. Atmospheric burners pump out energy to heat, well, the atmosphere. Yes, its true that atmospheric burners emit radiation as well, but the combustion here happens in air instead of a catalyst, so a lot more air is heated in the process. Now, when applying active ventilation with a fan, its easer to put an atmospheric roaster in "convective mode" by moving "already heated" air with more flux through the bean mass.

OTOH, with IR burners, you are basically just heating the drum surface, so the fan has a more limited convective effect since it needs bleed heat from the limited surface area of the drum to heat the air. This is basically what happens in a convection oven between baking and broiling modes: convection only works when baking and is effectively useless for broiling (some ovens even disable the convection fan when broiling).

My sense is that the Diedrich folks figured this out long ago when they committed to IR burners: by adding heat-exchanger baffling around their solid drums to increase the radiated surface area so as to allow the fan to more readily peel off surface heat for convection.

Now, with a perforated drum + IR burner design, this does not apply, since the radiation is point-to-point and most likely the most efficient: from burner-to-bean. In a way, the roaster is basically always in broiling mode, where the fan mainly comes into play, less for convection purposes than for heat dumping and chaff collection. I suspect that this why the IR version of the North Roaster comes with a perforated drum rather than a solid one. It is also this line of reasoning that perhaps answers why Mr. Li's prefers the stock version of the Huky with a perforated drum: it's a better match with his stock IR burner (In contrast, with my old Huky setup over my Bluestar gas range, using a solid drum made more sense for convective drum roasting).

It also makes total sense why the HotTop and Behmor (and even the electrical North) use wire/perforated drums: electrical elements are basically IR emitters that heat the beans directly with high efficiency (IOW, why waste energy heating a drum when you can heat the beans directly?). OTOH, this does little to explain the Quest - its a kind of design outlier from this perspective.